1. Field of the Invention
The present invention relates generally to drill string assemblies. More particularly, the invention relates to a dual wall drill string assembly for use in subsurface drilling applications.
2. Background and Description of the Prior Art
Drill pipe is used in various ways and for different applications including mining for precious gems, precious metals or coal; installing public and private utilities; drilling for oil and various gases including coal methane; creating an avenue to link the surface to one or more reservoirs; and linking a location on the surface or the subsurface with another surface or subsurface location. Accordingly, drill pipe comes in specialized configurations particularly adapted for use in one or more different applications. For example, drill pipe may comprise a single wall construction made from exotic steels to withstand hostile fluid and gases. Alternatively, drill pipe may comprise a dual wall construction adapted for use in reverse circulation drilling applications. Traditional drill pipe is “jointed,” i.e., it is made up of sections of pipe having opposing threaded ends. The pipe string typically is comprised of a series of pipe sections, which are screwed together by “tool joints” or upset connections. However, Flush Joint designs are becoming popular because of higher performance threads such as the “wedge threads”. Depending upon the application and environmental issues, a particular type of drill pipe may be preferable to another based upon cost, proven scientific principles, physical limitations and the like.
For example, coil tubing drilling is another technique utilized commercially at the present time. Coil tubing is not “jointed” in the sense of traditional drill pipe. Rather, a continuous length of manufactured tubing having an O.D. on the order of 1–3½ inches is spooled onto, for example, a 40 foot diameter reel. An injector head utilizing gripper blocks and a contra-rotating chain drive system is typically used to feed the coil tubing into the well bore. Coil tubing offers a number of advantages over conventional jointed drill pipe in some situations. These include the ability to drill and trip under pressure, faster trips, continuous circulation while tripping pipe, slim hole and thru tubing capability, a small location footprint, portability and a safer work area on the rig site.
More exotic drilling, completion and production operations also continue to evolve in the oil and gas industries. For example, drilling operations are now being conducted in regions of the arctic permafrost, and other regions, for methane hydrate. One source of methane hydrate is the world's sea beds where the combined actions of heat, pressure and time on buried organic material produce methane. Over the eons, organic rich source beds are converted into large quantities of oil and natural gas. Along with the oil, the natural gas (largely methane) migrates upwardly from sea beds due to its natural buoyancy. If sufficient quantities reach a zone of hydrate stability, the methane gas will combine with formation water to form methane hydrate. In some circumstances, these deposits can provide sufficient in-place resources as to be suitable for economic drilling and production.
Regardless of the application, conventional single-walled drill pipe and coil tubing have traditionally utilized the same basic drilling technique: fluids such as drilling muds are pumped down the inside of the pipe and cuttings produced by the drilling process are carried with the drilling mud to the earth's surface along the outside of the drill pipe. More particularly, the cuttings are carried out of the hole either between the borehole and the drill pipe or between a cased hole and the drill pipe. Some exotic types of drilling such as under balanced drilling deal with the pressure differential between the bottom hole pressures and the surface pressures. This method of drilling is controllable, but it is dangerous.
In addition, single-walled drill pipe exposes the borehole to the drilling mud or fluids until the borehole is cased or cemented. Further, when the returned drilling mud or fluids and cuttings pass along the drilled hole, the hole can become packed between the drill pipe and the hole from the cuttings, thereby limiting the movement of the drill pipe. One technique employed to overcome the problem of pipe sticking is to increase the mud flow volume and to circulate the borehole before further drilling is performed. This technique, however, impacts the earth's formation, for example, by forming or opening cracks in the formations. Typically, much, if not all of the additional mud flows into the cracks and/or produces additional cracks. In addition, when the hole is close to the surface, the additional mud can seep or flow to the surface in a process known as “fracing out,” which raises environmental concerns. Also it has been proven that low pressure gas wells are being abandoned because this process results in plugging and sealing off the avenue of producing natural gas. Reverse circulation air hammer drilling has produced low pressure gas wells, where previous standard drilled holes utilizing mud showed no evidence gas was present.
Reverse circulation drilling is a distinct drilling technique in which fluids are pumped to the drill bit and cuttings are transferred back to the earth's surface within the drill pipe assembly. This technique can be very advantageous because the drilling mud or fluid has limited exposure to the borehole and creates negligible damming effect. Also, it is environmentally-friendly in drilling applications that involve sensitive aquifers for drinking water and the like. The drill pipe typically used in reverse circulation drilling, however, is very stiff and difficult to steer and bend in a borehole. Thus, its use is limited to relatively straight hole applications, and it is not typically used in deviated hole drilling applications, which are commonly used in the construction, oil and gas, and mining industries.
In conventional drill pipes, wires are typically inserted and spliced inside each drill pipe to communicate with a gyroscope or compass transmitter in order to identify the location of the drill bit below the earth's surface. However, these wires are typically exposed and, therefore, are vulnerable to damage from short circuiting and breakage during the drilling operation.
It would be desirable, therefore, if an apparatus could be provided that would permit double-walled drill string pipe sections to be used for reverse-circulation, horizontal directional and deviated vertical drilling. It would also be desirable if a coil tubing apparatus could be provided which offered the advantages of such a double wall drill string. It would also be desirable if such an apparatus could be provided that would permit the double-walled drill string pipe sections to bend along the arcuate path of a subsurface borehole as freely as a single-walled drill pipe. It would be further desirable if such an apparatus could be provided that would convey larger-sized cuttings and increased volumes of cuttings from the drilling mechanism to the surface of the ground. It would be further desirable if such an apparatus could be provided that would permit drilling in soft, medium or hard rock formations as well as corrosive formations with reduced negative environmental impact and reduced borehole wall damage. It would be a further advantage if an apparatus was provided suitable for permafrost drilling operations, such as operations to drill and recover methane hydrate.
It would be further desirable if such an apparatus could be provided that would reduce or eliminate the risk of short circuiting the conductive wires on the drill string pipe sections. It would also be desirable if such an apparatus could be provided that would permit an operator at the ground surface to know immediately what rock or soil formation the drill is cutting as well as the condition of the drill bit. It would be still further desirable if such an apparatus could be provided that would produce a more efficient drilling mechanism by decreasing discharge back pressure experienced during drilling operations utilizing conventional drill pipe. It would be further desirable if such an apparatus could be provided that would achieve longer pilot borehole distances and have a longer lifespan in the borehole. It would also be desirable if such an apparatus could be provided to electronically sense the hole pressures and differential pressures between the ID and OD at close proximity to the drill bit, as well as at other appropriate locations along the drill string length. It would be further desirable if an apparatus could be provided to “smell” or detect hazardous gases, such as H2S, in the down hole environment. It would be still further desirable if such an apparatus could be provided that would permit the apparatus to be more easily assembled and perform drilling more efficiently, more quickly, and less costly. It would still further be desirable if such an apparatus could be provided to have an electric motor turn the drill bit instead of turning the drill pipe to limit or raise the fatigue life of the drill string. It would also be desirable if such an apparatus could be provided to be able to adjust the angle of the adjustable bent sub electrically, which can enable a bit, after drilling the hole with casing being installed simultaneously, to pull through the casing, leaving the casing in place. It would be further desirable if such an apparatus could be provided to have an electric motor(s) between the bit and bent sub, in order to deviate on a planned path so as to optimize the drilling task.
3. Advantages of the Invention
Accordingly, it is an advantage of the invention claimed herein to provide an apparatus that includes double-walled drill string pipe sections adapted for use in all subsurface drilling applications, it is another advantage of the invention to provide an apparatus having an inner tube adapted to bend to the arcuate path of a borehole with little or no resistance. It is also an advantage of the invention to provide an apparatus capable of conveying larger-sized cuttings and increased volumes of cuttings from the drilling mechanism to the surface of the ground. It is also an advantage of the invention to provide an apparatus that is capable of drilling in soft, medium or hard formations, permafrost formations, as well as corrosive formations with reduced negative environmental impact and reduced borehole wall damage. It is a further advantage of the invention to provide an apparatus that reduces or eliminates the risk of short circuiting the conductive wires on the drill string pipe sections. It is a still further advantage of the invention to provide an apparatus that permits an operator at the ground surface to know what rock or soil formation the drill is cutting and the location of the drill bit. It is also an advantage of the invention to electronically sense the hole pressures and differential pressures between the ID and OD at close proximity to the drill bit, as well as at other appropriate locations along the drill string length. It is another advantage of the invention to provide an apparatus that can detect the presence of hazardous gas, such as H2S. It is another advantage of the invention to provide an apparatus that produces a more efficient drilling mechanism by decreasing the incidence of “fracing out” of the subsurface formation. It is yet another advantage of the invention to provide an apparatus that achieves longer pilot borehole distances and has a longer lifespan in the borehole. It is a further advantage of the invention to provide an apparatus that is more easily assembled and performs all subsurface drilling more efficiently, more quickly, and less costly. It is a still further advantage to have an electric motor(s) turn the drill bit instead of turning the drill pipe to limit or raise the fatigue life of the drill string. It is a still further advantage to be able to adjust the angle of the adjustable bent sub electrically, which can enable a bit, after drilling the hole with casing being installed simultaneously, to pull through the casing, leaving the casing in place. It is a still further advantage to have an electric motor(s) between the bit and bent sub, so in order to deviate on a planned path so as to optimize the drilling task. Another aspect of the invention is the provision of a coil tubing apparatus which utilizes a “tube within a tube” design to achieve the aforesaid advantages of dual wall drill pipe. Additional advantages of the invention will become apparent from an examination of the drawings and the ensuing description.
4. Explanation of the Technical Terms
As used herein, the term “arcuate” refers to a curving, bending, turning, arching or other non-straight line, path or direction. As used herein, the term “arcuate path that is generally horizontal” refers to a borehole having an entry hole and a separate exit hole that are connected by a curved path. It is contemplated within the scope of the term “arcuate path that is generally horizontal” that the borehole may have a longer vertical component than its horizontal component.
As used herein, the term “conductive” means able to convey, transmit or otherwise communicate a signal and/or provide electrical current.
As used herein, the term “fluid” relates to a liquid, air, a gas, or a combination of liquid, gas, and/or air. The term “fluid” includes, without limitation, mixtures of solids and water, oils, other chemicals and the like.
As used herein, the term “signal” refers to a means for communication between a transmitter and a receiver. The term “signal” includes, without limitation, analog signals, digital signals, multiplexing signals, light signals and the like.
As used herein, the term “steerable” means the ability to follow the deviated path of a planned drilled hole.
As used herein, the term “substantially vertical borehole” refers to a borehole that is drilled substantially perpendicular to the earth's surface. The term “substantially vertical borehole” includes, without limitation, boreholes that are arcuate, curved and the like. It is also contemplated that the term “substantially vertical borehole” refers to a borehole that is a combination of vertical and horizontal drilling in relation to the earth's surface.
As used herein, the term “subsurface drilling” refers to any type of drilling, including vertical, horizontal and everything in between, employed by any industry that uses drill pipe to drill holes into the earth's formation, including, without limitation, soil, rock, ice, permafrost, wetlands, sand and the like.
The term “coil tubing” will be taken to mean any continuously-milled tubular product manufactured in lengths which require spooling onto a take-up reel during the primary milling or manufacturing process. Conventional coil tubing is constructed of carbon steel using the high-frequency induction welding process. Advanced metallic coil tubing strings are constructed using corrosion resistant alloys or titanium, with the seam weld formed using the TIG process.
The term “coil tubing unit” will be understood to mean an assembly of the major equipment components needed to perform a continuous-length tubing service or drilling operation. These basic equipment components generally include as a minimum an injector, service reel, control console, power supply, and well control stack assembly.